May 10, 2017 is Pesach Sheni - the 14th of Iyar. During the time of the Beit HaMikdash it on this date that those who were unable to participate in the Pesach service were able to bring a “make-up” Korban Pesach and then, that that evening, (the beginning of the 15th of Iyar), would eat it together with matzah and maror [Bamidbar 9:1-14].
But what about today, when tragically we do not have a Beit HaMikdash?
Chasidim have a custom to eat matzah on Pesach Sheni. However, while the prevalent custom is to eat matzah on the 14th of Iyar in commemoration of Korban Pesach (just as the afikomen on the night of the seder is a matzah eaten in commemoration of the Korban Pesach) there are those who maintain that the matzah should also be eaten on the same day as they once ate matzah - on the 15th of Iyar [See Darchei Chaim v’Shalom 531]. In fact, some Chasidim (Amshinov, Nadvorna, Kamarna) even drank four cups of wine [Nitei Gavriel Pesach 3:57 note 16]. However, the Vilna Gaon did not eat matzah on this date, and Rabbi Ephraim Greenblatt reports that the same was the case in Lithuanian Jewish communities [Maaseh Rav 181, Rivevot Ephraim 2:129].
Most communities do not recite tachanun and la’menatzeach on Pesach Sheini (and the mincha before) despite the fact that this custom is not mentioned in the Shulchan Aruch [see Shaarei Teshuva Orech Chiam 131:19 and Aruch HaShulchan Orech Chaim 131:12]. Some communities also omit tachanun on the 15th [Nimukei Orech Chaim 131:6 in the name of the students of the Arizal]; and some even do so for an entire week [Nitei Gavriel Pesach 3:57 note 8]!
A lesser-known custom on Pesach Sheni is a Sefardic custom to celebration (“hilula”) at the grave of Rabbi Meir Baal HaNes in Tiberias similar to the Lag Ba’Omer celebration at the grave of Rabbi Shimon Bar Yochai [Sdei Chemed c.v. Eretz Yisrael paragraph 6]. It is suggested that the timing of this celebration is that the first synagogue at his gravesite was dedicated on Pesach Sheni